1. Field of the Invention
This invention relates to a process for treating injection water used in enhanced oil recovery methods in order to prevent the growth of microorganisms in the water and oil.
2. Discussion of the Art
The problem of undesired growth of microorgansims in oil-bearing formations has plagued oil producers since the advent of waterflooding as a secondary oil production technique. Bacterial growth can result in souring of the crude oil in a reservoir, which is caused by the reduction of inorganic sulfate compounds to sulfides by certain bacteria. Plugging of the reservoir, wells, and related equipment can even result if such growth is substantial. In addition, equipment will quickly corrode if the metal is exposed to byproducts of microbial metabolism, particularly hydrogen sulfide.
Although several types of microorganisms are potentially deleterious to oil production, the major problems are caused by anaerobic sulfate-reducing bacteria (SRB), especially those of the genus Desulfovibrio. Further dissussion of microorganisms is provided in "The Role of Bacteria in the Corrosion of Oil Field Equipment", National Association of Corrosion Engineers, Technical Practices Committee, Pub. No. 3 (1976).
Other useful information can be found in Smith, R.S., and Thurlow, M.T., "Guidelines Help Counter SRB Activity in Injection Water", The Oil and Gas Journal, Dec. 4, 1978, (pp 87-91) and also in Ruseska, I, et al., "Biocide Testing Against Corrosion-Causing Oil-field Bacteria Helps Control Plugging", Oil and Gas Journal, Mar. 8, 1982, (pp 253-64). These sources generally recommend the use of a chemical microbiocide as part of a program to limit the growth of bacteria in oil fields or injection water.
Microorganisms in oilfields or in injection water are generally classified by their effect. Sulfate-reducing bacteria, slime-forming bacteria, iron-oxidizing bacteria, and miscellaneous organisms such as algae, sulfide oxidizing bacteria, yeast and molds, and protozoa can be encountered.
All of these microorganisms are capable of clogging filters and injection wells, and some can cause plugging of the rock formation if they can survive the temperatures and pressures found in the reservoir. In addition, certain organisms can liberate sulfide compounds which cause souring of the oil and corrosion of the wellpipe and other equipment. Unless precautions are taken to inhibit microbial growth, waterflooding can seriously diminish the value of the remaining crude oil.